1. Field of the Invention
The present invention relates to semiconductor integrated circuit manufacturing and, more particularly to a method of depositing the silicon nitride films using modified plasma enhanced atomic layer deposition (PEALD) at low temperatures (under 600° C., particularly under 400° C.).
2. Description of the Related Art
Silicon nitride layers deposited at low temperatures (under 600° C., particularly under 400° C.) have been used in a number of important applications for memory devices, for example, as a passivation layer, a surface protection layer, and/or a spacer for a transistor gate. Silicon nitride films may be formed by plasma enhanced chemical vapor deposition (PECVD) methods. The main advantages of the PECVD methods over other CVD methods are higher deposition rates and controllability over refractive indices in a wide range. A further advantage of the PECVD methods is that the process can take place at a relatively low temperature, for example, at temperatures under 600° C., particularly under 400° C., keeping minimum the total thermal budget of the cell processing. However, the PECVD methods for forming silicon nitride lead to poor conformality or poor step coverage on a substrate containing small features. In a small circuits and devises such as ultra-large scale integrated (ULSI) circuitries, such poor conformal coverage hampers the development of higher density circuit devices and elements.
In recent years, atomic layer deposition (ALD) and plasma enhanced atomic layer deposition (PEALD) methods have been investigated to improve conformality or step coverage of silicon nitride films on a substrate containing small features. However, the ALD or PEALD methods for forming silicon nitride lead to extremely poor deposition rates. Such poor deposition rates hamper lowering the manufacturing cost for development of higher density circuit devices and elements.